[llvm] [VPlan] Implement VPWidenCallRecipe::computeCost (NFCI). (PR #106047)

[Florian Hahn via llvm-commits]

fhahn wrote:

@aeubanks thanks for the report, it was the same issue as https://github.com/llvm/llvm-project/issues/107051: `setVectorizedCallDecision` did not consider forced scalars, meaning the VPlans created did not reflect the legacy cost decisions. Should be fixed now

https://github.com/llvm/llvm-project/pull/106047